In his first NBA start, he scored 37 points on 15-for-20 shooting against the Los Angeles Clippers—the most points ever scored in a game by an undrafted player in his rookie season—and grabbed 11 rebounds.[5] Morrow finished the 2008–09 season as the first rookie and first Warrior ever to lead the league in three-point field goal shooting, going 86-for-184 for a .467 percentage.[6]

Morrow re-joined the Warriors for the 2009 NBA Summer League, where he scored 47 points for the Warriors in a game against the New Orleans Hornets – setting the record for the most points scored by an individual in a game at the NBA Summer League.[7]

In the 13th game of the 2009–10 NBA season, Morrow set a new career high with 6 three pointers in a victory over the Dallas Mavericks.[8]

On July 16, 2014, Morrow signed a three-year, $10 million contract with the Oklahoma City Thunder.[15][16] On April 1, 2015, he scored a season-high 32 points on 11-of-16 shooting in a loss to the Dallas Mavericks.[17]